This invention relates to apparatus and operating techniques for converting crude methanol or the like to lower methyl tertiary-alkyl ethers. In particular, this invention relates to an integrated system for converting crude methanol to valuable products by etherifying lower branched olefins, such as C.sub.4 -C.sub.7 normally liquid iso-olefins. It is known that isobutylene and other isoalkenes produced by hydrocarbon cracking may be reacted with methanol over an acidic catalyst to provide methyl tertiary butyl ether (MTBE) and isoamylenes may be reacted with methanol over an acidic catalyst to produce tertiary-amyl methyl ether (TAME). Those ethers having the formula CH.sub.3 --O--R, where R is a tertiary alkyl radical, are particularly useful as octane improvers for liquid fuels, especially gasoline.
MTBE and TAME are known to be high octane ethers. The article by J. D. Chase, et al., Oil and Gas Journal, Apr. 9, 1979, discusses the advantages one can achieve by using these materials to enhance gasoline octane. The octane blending number of MTBE when 10% is added to a base fuel (R+O=91) is about 120. For a fuel with a low motor rating (M+O=83) octane, the blending value of MTBE at the 10% level is about 103. On the other hand, for an (R+O) of 95 octane fuel, the blending value of 10% MTBE is about 114.
Increasing demand for high octane gasolines blended with lower aliphatic alkyl ethers as octane boosters and supplementary fuels has created a significant demand for isoalkylethers, especially the C.sub.5 to C.sub.7 methyl alkyl ethers, such as methyl tertiary butyl ether (MTBE) and tertiary amyl methyl ether (TAME). Methanol may be readily obtained from coal by gasification to synthesis gas and conversion of the synthesis gas to methanol by well-established industrial processes. As an alternative, the methanol may be obtained from natural gas by other conventional processes, such as steam reforming or partial oxidation to make the intermediate syngas. Crude methanol from such processes usually contains a significant amount of water, usually in the range of 4 to 20 wt. %; however, the present invention is useful for removing water in lesser amounts or greater.
It is the main object of the present invention to provide a novel and economic technique for removing excess water from crude methanol feedstocks, including novel operating methods and equipment for treating these oxygenate feedstocks prior to etherification and disposing of raffinate containing methanol. It has been discovered that aqueous methanol streams, such as etherification feedstock extraction byproduct can be economically upgraded by catalytic conversion concurrently with hydrocarbons.